[A-HW25] Near Surface Investigation and Modeling for Groundwater Resources Assessment and Conservation

[AHW25-05] Investigating water storage dynamics using gravimetry in the Choushui River Alluvial Fan, central Taiwan

*KUANHUNG CHEN^1,2, Cheinway Hwang² (1.Department of Earth and Planetary Science, The University of Tokyo, Japan, 2.National Yang Ming Chiao Tung University, Taiwan)

Keywords:Groundwater, Gravimetry, Geophysical investigation , Land subsidence , Recharge , Taiwan

The Choushui River Alluvial Fan (CRAF) is full of groundwater resources but faces severe land subsidence at the middle fan due to overpumping. The water resource agency of Taiwan attempted to recharge surface water artificially from proximal fan to reduce the extent of land subsidence. Investigations for regional-scale groundwater systems before constructing artificial ponds require many budgets. However, typical hydraulic tests, such as pumping and infiltration tests, are site-dependent and do not fit the scope of management practice. On the contrary, gravimetry can passively detect water storage dynamics on a regional scale using natural events, reducing the cost of manually pumping or injecting water at a specific site. This study set up several absolute gravity sites at proximal and middle fans across the Choushui River Alluvial Fan. We estimated the unsaturated and saturated water storage dynamics using seasonal gravity changes. Besides, observed gravity changes at each site reveal that hydrogeological investigations were still insufficient and required more effort in the future as aquifer heterogeneity exists in the CRAF. The advantages and potential of gravimetry applied to hydrology investigations will be shown in this presentation.